This invention relates generally to lifting devices for use on a temporary basis to lift heavy things up to, or to lower them down from, an elevated heightxe2x80x94in particular the roof of a building; more specifically, it relates to an attachment for a sturdy ladder in order to take advantage of the structural strength of the ladder.
There are many instances in which a relatively heavy load must be raised from the ground to an elevated height, such as the roof of a building. For example, an air conditioning repair man may need to raise a new compressor to the top of a buildingxe2x80x94to replace one that has worn out. Similarly, the worn-out compressor must later be safely lowered to the ground, without posing a risk to anyone or any thing at ground level. A compressor rated at three tons of cooling capacity will often weigh about 50 pounds, and a five ton compressor will often weigh about 100 to 150 pounds. Another heavy thing that is often raised to the top of a building is roofing material that can be both heavy and bulky.
When an air-conditioning service man goes out on a service call, he often goes alone, because initially he doesn""t know whether the problem is likely to be a simple thing to fixxe2x80x94like resetting a circuit breaker, or a more complicated thingxe2x80x94like replacing a compresssor. If he normally works alone, and he discovers only after arriving at a job site that heavy lifting will be required, he may have to call for assistancexe2x80x94because he needs muscular help to lift a heavy compressor to the elevated height of a roof-mounted system. Waiting for an assistant to arrive can be wasteful of time on the part of the service man, and it can also be frustrating to the customer. On a hot day, a client normally wants cool air restoredxe2x80x94not an explanation as to why the job will have to be completed tomorrow instead of today.
This kind of a problem is not new, of course, and efforts have been made to solve the problem. One proposed solution is found in U.S. Pat. No. 5,139,108 to Pate entitled xe2x80x9cStabilized Ladder Power Winch System,xe2x80x9d in which a winch is affixed to a ladder near the bottom of the ladder; a long cable is used to extend from the low winch all the way to the top of the ladder, over a pully and then back down to the load that is to be raised. Although it does not appear in the Pate drawings, there will of necessity be two people in a work crew using a Pate apparatus. That is, there must be one person standing on the ground and controlling the winch, and another person on the roof guiding the load as it is lifted to the point where it reaches the roof. U.S. Pat. No. 4,598,795 to Larson entitled xe2x80x9cLadder Hoist Attachmentxe2x80x9d avoids the two-man problem faced by Pate by placing a hand-cranked winch at the top of the ladder, so that a single worker could presumably get a heavy load to the roof and control it once the load had arrived. However, a hand-cranked winch will require that the worker use a crank in the manner in which all cranks are used. This means that circular movement of the crank will cause the worker to be pushing out on the crank (and the attached ladder) during half of a cycle, and pulling in on the crank (and the attached ladder) during the other half of a full cycle. This alternate pushing out and pulling in on the ladder is not conducive to control of either a stable ladder or a heavy load that is suspended from the top of the ladder by a long cable. Indeed, the oscillatory movement of the crank can result in oscillations that are imparted to the load, with the result that the load can begin to swing to and fro from a long cable that extends to the roof.
Another deficiency of all of the aforementioned devices is that they are adapted to work only at the periphery of a building, i.e., where the foot of a ladder is resting on the groundxe2x80x94spaced from but fairly close to the edge of a building. There is no teaching in any of the patents as to how their respective devices might be used in the middle of a building with a flat roof, when a roof-access opening is located near an elevator shaft and an interior elevator has been used to get a heavy load to the top floor of a building. What remains is the problem of getting the load from the building""s top floor onto the roof, and the only travel path is through a central opening in the roof. It is an object of this invention to provide an apparatus that can be used either at the periphery of a building or at an interior position where there is an access opening in the roof.
In brief, the invention includes a structural frame that is adapted to be temporarily affixed to a heavy-duty ladder. An ordinary definition of the word xe2x80x9cladderxe2x80x9d is a rigid structure, often portable, consisting of two long xe2x80x9csidexe2x80x9d members connected by a series of spaced and parallel rungs or steps; the rungs or steps are usually about 18 to 24 inches long. For the purposes of this disclosure, ladders can be further identified as being of three principal types. One type is generally straight or linear, like a ladder of fixed length or an extension ladder; such ladders are not inherently stable when they are erect, and it is expected that they will be connected to or lean against something for at least a part of their vertical stability. As seen from the side of a ladder in a working position, a straight ladder and the wall against which it is leaning will have the general shape of a letter A that is leaning significantly to one sidexe2x80x94like the Tower of Pisa.
A second type of ladder has two pairs of legs of essentially equal length; one pair of legs is usually pivoted to the other pair at the ladder""s top. Such ladders are normally self supporting, in the sense that they don""t have to lean against a wall or the like to be usable. An example of the second type of ladder is commonly called a step ladder, and it resembles the letter xe2x80x9cAxe2x80x9d in a symmetrical form when seen from the side. Step ladders usually have narrow steps instead of rungs for supporting a person""s feet, and they are usually shorter than straight ladders.
The third kind of ladder is articulated or folding, sometimes called a multipurpose ladder; it may be configured into a variety of different shapes, depending upon the requirements of the user and the environment in which it will be used. For example, an articulated ladder may be configured as an inverted xe2x80x9cUxe2x80x9d or a scaffold, and used by a house painter to straddle a hedge that is growing immediately next to a house. This invention is usable with all of these ladders.
A major part of the invention ia a structural frame that functions as a platform that is designed to be placed with a generally horizontal orientation somewhere near the top of a ladder. In one mode of use, the structural frame functions as a long handle that is used to push a straight ladder away from the edge of a roofxe2x80x94on a temporary basis, so that a load can be lifted onto the roof. Another important structural piece is a brace that preferably is foldable so that it may be made to lie in the same general plane of the platformxe2x80x94during transportation and storage; this configuration will sometimes be referred to aptly as its xe2x80x9cflatxe2x80x9d or storage configuration. The brace can also be unfolded for use in stablizing the platform when a straight ladder is generally upright and leaning against the side of a building, etc. When the platform is being held with a generally horizontal orientation, its rearward end will be engaged with one rung of the ladder. The brace will extend downwardly at an angle with respect to the platform, to make load-bearing contact with and xe2x80x9cengagexe2x80x9d a different rung of the ladder at a lower elevation.
Mounted on and carried by the structural frame is an electrically powered winch which is selectively actuated to raise or lower a heavy-duty cable and any load to which the cable is attached. Actuation of the winch is preferably accomplished with a rocker-type switch that is located at the forward end of the structural frame. The preferred switch may also be described as a double pole, normally OFF, momentarily ON switch, in that the winch""s motor is actuated for only as long as the switch is depressed, whether a load is being raised or lowered.
When in its flat mode, the lifting apparatus can be carried up a straight ladder by a worker, who then connects it to the ladder when he (or she) has reached the roof and climbed onto it. The lifting apparatus (including a winch and cable, etc.) is expected to weigh about 30 pounds when the structural parts are made of aluminum tubing, and this is a weight that a healthy worker is expected to be able to handle without difficulty. When the lifting apparatus has been carried to the roof, it is easily attached to an upper part of the ladder, and the cable is ready to be played out until sufficient length to reach the ground has been obtained. A hook at the distal end of the cable is then connected to a load on the ground. When a source of electrical power, usually 110 volt AC power, has been connected to the winch, the load is ready to be lifted toward the roof. Any needed clearance between the generally vertical cable and the edge of the roof can be realized by manually pushing the top of the ladder away from the roof for a foot or so.
When the load rises to the point that it is almost at the roof, the ladder may need to be pushed outward for another few inchesxe2x80x94to ensure that there is clearance for the load. Once the load is at an elevation above the roof, the ladder may be allowed to lean inward until it again contacts the edge of the roof, and the load may then be lowered to the roof.
Alternatively, a load may be brought to a building""s roof by pulling it upward through a roof-access opening in the interior of the roof. Such openings in roofs are often closed by skylights at most times, but they can be opened to provide access to the roof for workers. A step ladder, or two step ladders, can be erected adjacent the opening, and the lifting apparatus can be installed in its flat modexe2x80x94between two structural members on the ladder(s) that are at about the same height. The winch""s cable can then be lowered through the access hole and connected to a load (inside the building) that is to be brought up to the roof. Of course, the ladders that are selected for use with this invention should be sturdy enough to carry the loads that may need to be lifted to (or lowered from) a roof. The preferred winch has a load rating of at least 200 pounds, so any ladder that is used with the invention should be rated to carry a similar load.
Another advantageous feature of the invention is a safety device that prevents the structural frame from becoming accidentally separated from the ladder during use. This is important because it is not a goal of the invention to build a cousin or other close relative of the Eiffel Tower; rather it is a goal to safely lift a load to and from an elevated height, even if only one person is available to do the lifting. Hence, a quick and easy set-up of the apparatus is important, but speed must not compromise safety. With this apparatus the initial step of connecting the frame to the ladder is done by simply letting a C-shaped structural member descend over an upper rung of a ladder. Next, a safety pin is inserted into two prepared holes near the outer edges of the C-shaped member, thereby capturing the ladder""s rung and holding it until the pin is manually removed. This prevents the accidental separation of the frame and the ladder until all lifting has been completed.